An image display device fixed to the head or face of a user who observes an image, or a head mount display, is known. The head mount display is equipped with an image display unit for each of the left and right eyes, for example, and configured to perform visual and audio control in cooperation with headphones. The head mount display attached to the head in a manner completely blocking the external environment increases virtual reality during viewing. The head mount display further has a function of displaying images different for each of the left eye and the right eye, and therefore is capable of displaying parallactic images for the left and right eyes to present a 3D-image.
This type of head mount display forms a virtual image on the retina of the eye as an image to be observed by the user. When an object is located in such a position that the distance between the object and a lens becomes shorter than the focal distance, a virtual image is formed on the object side. For example, a head mount display currently proposed positions a wide-view-angle virtual image optical system in front of the pupil with a distance of 25 millimeters from the pupil, and positions a display panel having an effective pixel range of approximately 0.7 inch in front of the wide-view-angle optical system to form an enlarged virtual image of a display image on the pupil of the user (for example, see Patent Document 1).
Moreover, the user wearing this type of head mount display is capable of observing an image cut from a wide-view-angle image. For example, there has been proposed a head mount display which realizes a 360-degree image of a whole space following a motion of the head of the user by using a head action tracking device constituted by a gyro sensor or the like and attached to the head of the user (for example, see Patent Document 2 and Patent Document 3). According to this method, an image following a motion of the head is reproduced by shifting the display area within the wide-view-angle image in such a direction as to cancel the motion of the head detected by the gyro sensor. In this case, the user experiences an overlook throughout the space.
It is preferable that the image presented by the head mount display follows the motion of the head of the user with higher accuracy. When tracking of the motion of the user is inaccurate, the image presented to the user may become an image inaccurately following the motion of the head of the user, or giving discomfort to the user.